The behavior of such cells having a thin layer of cholesteric medium normally depends in part upon the molecular orientation of the cholesteric layer at its major surfaces. Two particular types of alignment are `homeotropic alignment` in which the molecules are aligned normal to the layer surface, and `homogeneous alignment` in which they are aligned in the plane of the surface. In the case of homogeneous alignment this alignment will be termed homogeneous parallel alignment in the case where the alignment is in a particular direction in the plane of the surface.